Field
Embodiments of the present invention are generally directed to systems and methods of controlling a relay, and more particularly to systems and methods of controlling a relay or multiple relays with reduced power dissipation.
Discussion of Related Art
Many electronic devices and circuits include one or more relays for various purposes, such as controlling electric motors or lighting, controlling a high voltage circuit such as an audio amplifier with a low voltage signal, controlling a high current circuit such as the starter solenoid of an automobile with a low current signal, etc. In an uninterruptible power supply (UPS), relays may be used for input switching, to switch from operating under AC power to operating under battery (DC) power, for back-feed protection, or for other purposes.
FIG. 1 illustrates a conventional Form C relay (also called a change-over relay or a single pole double throw (SPDT) relay) that may be included an electronic device, such as a UPS system, as well as a typical control circuit for controlling the relay. As shown in FIG. 1, the relay 100 includes a Common (C) terminal 101, a Normally Closed (NC) terminal 102, a Normally Open (NO) terminal 103, a voltage supply terminal 104, a control terminal 105, and a coil 106. In a device such as a UPS where the relay 100 is used for back-feed protection or input line switching, the common terminal 101 might be electrically coupled to a line output terminal (e.g., a hot output terminal or a neutral output terminal) of an AC power source, the NO terminal 103 electrically coupled to a device input terminal of the UPS, and the NC terminal 102 left unconnected, or used for feedback or some other purpose. The voltage supply terminal 104 of the relay 100 would typically be electrically coupled to a suitable voltage source capable of energizing the relay, and the control terminal 105 of the relay would typically be electrically coupled to ground through a switch 110, such as a MOS transistor, as shown in FIG. 1.
Where it is desired to energize the relay 100, a control signal (S1) is asserted on a control terminal 111 of the switch 110 to close the switch thereby electrically coupling the coil 106 of the relay between the voltage source and ground. The current in the coil of the relay electrically couples the common terminal 101 of the relay to the NO terminal 103 and remains in this position until the control signal is de-asserted.